Designing a WikiHouse to resist wildfires

I live in Portugal at the moment and wildfires are an increasing concern. Which has had me thinking about how one would go about hardening a WikiHouse design against wildfires. Here’re a few thoughts after reading various online resources, with one assumption being that you’re designing a detached building.

Site layout and defensible space

  • Situate the building as far as you can from adjacent woodland and place incombustible material between—such as patios, pools, driveways and low fire-retardant plants—while paying particular attention to areas downhill of the building.
  • Provide sufficient access for fire tender vehicles, preferably with a turning area.

Protect against embers

  • Embers can float into cavities and openings and ignite a fire.
  • Use ember-resistant vent grilles (they’re protected with a micro filter metal mesh) and/or consider fire dampers which can be closed manually or by a fusible link that melts at a certain temperature.
  • Use cladding and roofing finishes that don’t leave gaps. Use sheet materials without gaps or snugly interlocking tiles. Rainscreen venting should be protected with fine metal insect mesh that doubles up as protection against embers.
  • Avoid gaps between bottom of external wall and ground level, to ensure embers do not make their way under the building.

Fire resistant envelope

  • Consider incombustible cladding materials, such as brick, adobe, stone, clay tile, slate, metal and incombustible sheet materials (such as cement board, calcium silicate, gypsum fibre boards) when cladding walls, roofs and soffits. These choices will need to be balanced against local availability of materials and the carbon footprint of transporting heavy materials.
  • Steeper roofs will encourage embers to roll off and away from the building. Flat roofs will retain them.
  • A well designed and well maintained green roof can provide protection against wildfire. See more here
  • Consider adding mineral wool sheathing insulation. Sheathing insulation—insulation fitted to the external face of the WikiHouse frame before any cladding—will be a consideration if you’re aiming for Passivhaus performance, but it could also be used to protect the main structure against heat and fire.
  • Glass will typically fail quickly in extreme heat. Double or triple glazing with tempered glass will fair best. But the best form of protection is to install external metal roller shutters to all windows, which can be closed manually or by a fusible link that melts at a certain temperature.
  • Install fire-rated external doors and/or consider metal roller shutters as above.
  • Consider melt-resistant or incombustible infill insulation. If a fire has made its way beyond the breather membrane then it’s probably just a matter of time before fire makes its way inside, whether you’ve used incombustible insulation or not. But by using an incombustible—or at least a melt-resistant infill insulation—you may guard against damage to the main structure in the event of extreme heat.
  • Consider an intumescent breather membrane, while bearing in mind that these are designed to increase the time for building occupants to escape, rather than protect the building from permanent damage. If the intumescent membrane is activated as the result of a wildfire it’s probably just a matter of time before fire makes its way inside. But it could potentially act as the final line of protection that protects the main structure from critical damage, leaving you with a building that require repairs to the external finishes only, rather than the structure as well.

Fire suppression

  • Consider installing a sprinkler system with heads on the roof, over decks, patios and balconies. Preferably powered by off-grid source of power.
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This is a really interesting reflection and something I had not thought about yet but it absolutely makes sense to consider and research it, especially with climate change causing more extreme weather events and droughts leading to more wildfires. @Mel perhaps it’s worth including a section on this in the general WikiHouse documentation and design guides?

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Thanks Jenn.

One other thing comes to mind, as a result of a recent experience with wildfire is the comfort and wellbeing of people inside the building; protecting the air inside a home when there are wildfires close enough to pollute the air, but not close enough to evacuate.

This year there was a wildfire in a municipality next to ours and this was enough to make the air unpleasant to breath; we woke up one morning and it smelled like smoke and dampened fire.

Fortunately we had also just replaced our windows. The original windows were very inefficient sliding windows with very little in the way of airtightness. Unlike the neighbouring flats we were able to shut our windows tight and keep the smoke out for the next couple of days.

We’re yet to install trickle vents (they’re going to fitted to the internally exposed face of the roller shutter box) but had they been installed I would have shut those too.

This got me thinking about filtration of incoming air. Pretty easy if you’re installing whole house ventilation with one intake, and certainly something to consider, but I had never come across filters for trickle vents.

But I did find a company in Poland that makes such vents. You can check em out here:

Surface mounted:

Over the window:

About £40-50 each.

Filter types here:
https://brevis-ventilation.com/produkty/urbino-filters/

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I totally get what you mean. I think air pollution is such an important issue to consider and not enough people are talking about it.

We currently live in London, England and it’s a real issue for us here. Not because of wildfires though. We’re about to move to a town (buying our first home) and on top of our priority for the new house is to install mechanical ventilation. This will require us to improve the house insulation and then that will allow for a well-managed ventilation and filtration system to be installed. Mechanical ventilation is something we have learned about while exploring the WikiHouse principles and wider sustainable home designs.

Basically what we’re trying to do is to test different ways of having a more sustainable and healthy home within our current living environment. We still very much have the ambition to one day build our own home with WikiHouse, but until that day comes (funding, land ownership and designs permitting), we will try to retrofit as much as we can. Again I think the WikiHouse sustainable design principles are so important for this. @Mel this may actually be an interesting topic to explore in a community event?

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@JennHuygen - yes we are going to be updating the guides next year and will definitely be including a section on fire, @Gabriele is doing some work on that at the moment. Also, we have started to think about 2023 events and I’ve added your suggestion to the list - thanks! Please shout with any other requests for topics!

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